This invention relates to a pin retractor for semi-trailer tandems, and a method of retracting the pins on a semi-trailer tandem. Trucks are used to transport a great variety of products. Many trucks comprise a tractor attached to one or more semi-trailers. A typical tractor is provided with a front set of wheels to steer the tractor, and one or more rear axles. The engine of the tractor typically drives the rear axles. The semi-trailer immediately behind the tractor is typically attached to the tractor by means of a fifth wheel, which is positioned on the tractor above the rear axle or axles. Semi-trailers are provided with a tandem, which may comprise one or more axles. In most semi-trailers, the tandem can be slid backward and forward to adjust the load on the rear axle or axles.
A typical semi-trailer is provided with two rails at the rear and on the bottom of the cargo surface. The sliders of the tandem are adapted to be received between the rails, such that the tandem cannot slide from side to side. However, the tandem is adapted to slide backward and forward along the rails.
When a semi-trailer is being moved down a roadway by a tractor, the tandem must be secured in a fixed position. This is typically achieved by a plurality of pins. Each pin is attached to the tandem such that the pin can move sideways, but not backward or forward. The rails on the semi-trailer contain a plurality of apertures, adapted to receive the pins. A typical tandem is provided with two sets of pins, one at the front and one at the rear. In each set of pins, one is on the left side of the semi-trailer and one is on the right side of the semi-trailer. When the pins are in the extended position, each pin fills an aperture in one of the rails, and thereby prevents forward or rearward movement of the tandem relative to the rails. When the pins are in the retracted position, they do not engage any of the apertures in the rails, and the tandem can be slid backward or forward on the rails. The range of movement of the tandem is usually restricted by a front stop and a rear stop, which prevent the tandem from sliding so far that it becomes disengaged from the rails.
The ability to move the tandem relative to the cargo surface of the semi-trailer is desirable for a number of reasons. When a tractor and semi-trailer must maneuver around city streets, relatively tight corners are frequently encountered. By moving the tandem forward, it is easier to negotiate tight corners. When a tractor and semi-trailer are traveling on highways, moving the tandem toward the rear puts a larger percentage on the load on the axles of the tractor, thereby providing a better ride.
Semi-trailers in current use typically have only a manual means for adjusting the position of the tandem relative to the cargo surface. In order to slide the tandem of such a semi-trailer, a number of steps are necessary: (1) the driver applies the brakes of both the tractor and the semi-trailer; (2) the driver climbs out of the tractor and pulls the pin release lever which is normally immediately in front of the left wheel or wheels on the front axle of the tandem; (3) the driver returns to the cab and releases the brakes on the tractor; (4) the tractor is then driven either forward or backward thereby moving the cargo surface of the semi-trailer on the tandem (the tandem remains stationary because the brakes on the tandem have not been released); (5) once the desired position of the tandem is achieved, the driver applies the brakes of the tractor; (6) the driver leaves the cab of the tractor and pushes the pin release lever in, so as to engage the pins of the tandem into the apertures on the rails, thereby locking the position of the tandem relative to the cargo surface of the semi-trailer; (7) the driver then returns to the cab of the tractor, releases the brakes on the tractor and the semi-trailer, and drives away.
In practice, a number of problems are common in this procedure. For example, the pins frequently become stuck in a specific position. The driver can try to remedy this condition by applying the brakes of the tandem, and then driving the tractor backward and forward slightly, so as to rock the tandem. This back and forth motion can damage the clutch, drive line and rear end of the tractor. In extreme cases, a second person may be necessary to pull on the pin release lever while the driver is using the tractor to rock the tandem back and forth. The person who is pulling on the pin release lever during such a maneuver is in a relatively dangerous position.
Another problem frequently encountered in positioning a tandem relative to the cargo surface of a semi-trailer, is the difficulty in positioning the tandem such that the pins are in alignment with apertures on the rails. This sometimes leads to a repetition of steps (3), (4) and (5) described above, until the pins are in a position to be received by the correct apertures when the pin release lever is pushed.
The advantage of a pin retracting mechanism for a semi-trailer which is pneumatically, as opposed to manually, powered is recognized in the prior art. For example, U.S. Pat. No. 4,286,797 dated Sept. 1, 1981 to Mekosh et al., (the disclosure of which is hereby incorporated by reference) discloses a pin retracting mechanism for a trailer. However, the mechanism disclosed by this patent cannot be economically used in most of the tandems of semi-trailers in current use, because extensive structural modifications of the tandem would be required.